Organopolysiloxane composition having ceramic microspheres

Abstract

A composition comprising a reactive polysiloxane and a hydroxyl-containing precursor, a flame retardant, and micron-sized hollow ceramic particles, the composition being useful in the preparation of an insulating, compressible, and flame resistant foam material useful for providing thermal insulation, flame resistance, and compressibility for applications such as lithium ion batteries.

Description

Technical Field

[0001] The present invention relates to an organopolysiloxane composition containing micron-sized ceramic particles.

Background Art

[0002] Rechargeable lithium-ion batteries (LiB) are commonly used in various applications including electric vehicles (EV) and grid energy storage systems. LiB has desirable properties such as high energy density and stability, but its practicality is currently limited due to safety concerns. First, the failure of a LiB cell can be caused by manufacturing defects, internal short circuits, overheating, overcharging, or mechanical shock. Second, the heat generated from a failed cell can propagate, thereby causing thermal runaway in adjacent cells. The rapid pressure increase resulting from these thermal events increases the risk of fire and explosion.

[0003] Thermal runaway can be mitigated by placing a thermal barrier that provides thermal insulation and flame resistance between cells in a LiB module. Commonly used thermal barriers such as aerogels, ceramic fibers, and mica boards provide such properties, but aerogels and ceramic fibers lack mechanical elasticity, while mica boards lack compressibility. On the other hand, silicone blown foams are suitable for low and medium energy density batteries because they provide appropriate compressibility, but they have a problem of insufficient thermal insulation to prevent thermal runaway in very high energy density battery packs. Therefore, in the field of thermal barriers for rechargeable batteries, it is desirable to create a barrier that provides thermal insulation, flame resistance, and satisfactory compressibility.

Summary of the Invention

[0004] The present invention provides, based on the weight of the composition, a) 2 to 50 weight percent of a polysiloxane functionalized with at least two Si-H groups and having a degree of polymerization in the range of 5 to 1000; b) 1 to 50 weight percent of water, alcohol, diol, polyol, or a compound containing one or more silanol groups; c) 10 to 90 weight percent of a polysiloxane functionalized with at least one ethylenically unsaturated group and having a degree of polymerization in the range of 20 to 2000, (the total concentration of components a, b, and c is in the range of 35 to 95 weight percent based on the weight of the composition) d) a catalytic amount of a hydrosilylation catalyst; e) 1 to 30 weight percent of a flame retardant; and f) 1 to 35 weight percent of hollow ceramic particles having a volume average particle diameter in the range of 25 μm to 300 μm, to address the needs in the art.

[0005] The composition of the present invention is useful for providing a foamed material as a compressible, heat-insulating, and flame-resistant spacer in lithium-ion batteries.

DETAILED DESCRIPTION OF THE INVENTION

[0006] The present invention provides a composition which, based on the weight of the composition, comprises a) 2 to 50 weight percent of a polysiloxane functionalized with at least two Si-H groups and having a degree of polymerization in the range of 5 to 1000; b) 1 to 50 weight percent of water, alcohol, diol, polyol, or a compound containing one or more silanol groups; c) 10 to 90 weight percent of a polysiloxane functionalized with at least one ethylenically unsaturated group and having a degree of polymerization in the range of 20 to 2000, (the total concentration of components a, b, and c is in the range of 35 to 95 weight percent based on the weight of the composition) d) a catalytic amount of a hydrosilylation catalyst; e) 1 to 30 weight percent of a flame retardant; and f) 1 to 35 weight percent of hollow ceramic particles having a volume average particle diameter in the range of 25 μm to 300 μm.

[0007] The polysiloxane (a) functionalized with at least 2, preferably at least 3 Si-H groups has a degree of polymerization in the range of 5 to 1000 or ~500 or ~200. The hydroxyl-containing compound (b) is preferably benzyl alcohol or a C 2 ~C 8 -alkyl diol. The polysiloxane (c) functionalized with at least 1, preferably at least 2 ethylenically unsaturated groups has a degree of polymerization in the range from 20 or 100 or 200 or 300 to 2000 or 1500 or 1000. The total weight percentages of components a, b, and c range from 35 or 50 to 95 weight percent based on the weight of the composition.

[0008] The polysiloxane functionalized with at least 1 ethylenically unsaturated group is preferably functionalized with 2 C 2 ~C 8 -alkenyl groups, more preferably 2 vinyl or 2 allyl groups. The polysiloxane functionalized with at least 1 ethylenically unsaturated group is most preferably a polydimethylsiloxane functionalized with 2 vinyl groups. The polydimethylsiloxane functionalized with 2 vinyl groups is advantageously designed to have a viscosity in the range of 10,000 to 50,000 mPa·s. This viscosity is conveniently achieved by combining divinyl-functionalized polydimethylsiloxanes of different degrees of polymerization, i.e., by a bimodal distribution of divinyl-functionalized polydimethylsiloxanes.

[0009] The hydrosilylation catalyst is preferably a platinum-based catalyst such as chloroplatinic acid and is used in a catalytic amount, typically in the range of 0.5 ppm to 200 ppm of Pt based on the weight of the composition.

[0010] The composition also contains a flame retardant in an amount from 1 or 2 or 3 weight percent to 30 or 20 or 15 weight percent, and the flame retardant is a metal hydroxide, carbonate, hydroxide-carbonate, or hydrate that releases CO 2 or water or both upon heating. Examples of flame retardants include Al(OH) 3 、Mg(OH)2 , Ca(OH) 2 MgCO 3 ·3H 2 O (nesquehonite), Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O (hydromagnesite), MgCa(CO 3 ) 2 (huntite), AlO(OH) (boehmite), NaHCO 3 , and hydrated MgSO 4 (epsomite) are included.

[0011] The composition further comprises hollow, air-filled, or inert gas-filled ceramic particles from 1 or 5 or 10 weight percent to 35 or 30 - 25 weight percent. As used herein, "ceramic" refers to crystalline or semi-crystalline inorganic oxides, nitrides, carbides, oxynitrides, or oxycarbides of metals such as aluminum (e.g., crystalline or semi-crystalline Al 2 O 3 ), silicon (e.g., crystalline or semi-crystalline SiO 2 ), or calcium (e.g., crystalline or semi-crystalline CaO), or combinations thereof. The crystallinity can be measured by X-ray powder diffraction. As used herein, the term "semi-crystalline" refers to a ceramic material having both amorphous and crystalline regions. The hollow ceramic particles have an average volume particle size from 25μm, or from 50μm, or from 70μm to 300μm, or up to 200μm, or up to 150μm when measured using a dynamic light scattering analyzer such as a Beckman Coulter LS 130 Particle Size Analyzer. The resulting article has a density in the range from 0.10 or 0.15 g / cm 3 to 0.90 or 0.50 g / cm 3 .

[0012] The composition is useful for preparing polyorganosiloxane foam articles substantially as described in, for example, U.S. Patent No. 5,358,975. Advantageously, a polysiloxane functionalized with at least three Si-H groups is contacted in the presence of a) an alcohol, diol, polyol, or silanol, and b) a divinyl-functionalized polydimethylsiloxane and a platinum-based catalyst to form -Si-CH 2 -CH 2 -Si- groups and -Si-O-R groups (wherein R is a structural unit of an alcohol, diol, polyol, or silanol, i.e., the reaction product) to form a crosslinked network of organopolysiloxane.

[0013] It may be advantageous to prepare the foam material using a two-part approach as follows. In a first container, a first portion of a divinyl-functionalized polydimethylsiloxane, a first portion of a flame retardant, a platinum-based catalyst, a hydroxyl-containing compound or compounds, and a first portion of hollow ceramic particles are blended to form a Part A composition. In a second container, the remaining portion of the divinyl-functionalized polydimethylsiloxane, a polymer resin blend that is a mixture of a divinyl-functionalized polydimethylsiloxane and a crosslinked organopolysiloxane resin, the remaining portion of the flame retardant, a polysiloxane functionalized with at least three Si-H groups, and the remaining portion of the hollow ceramic particles are blended to form a Part B composition. Then, Part A and B are combined, mixed, and then injected between two release film sheets to form the foam material of the present invention.

[0014] Accordingly, in another aspect, the present invention is a foam material having heat insulation, compressibility, and flame resistance, comprising, based on the weight of the foam material, 35 to 95 weight percent of a polyorganosiloxane foam, 1 to 30 weight percent of a flame retardant, and 1 to 35 weight percent of hollow ceramic particles having a volume average particle size in the range of 25 μm to 300 μm, and having a density in the range of 0.10 to 0.90 g / cm 3 The foam material has a density in the range of.

[0015] In yet another aspect, the present invention is a battery module comprising a shell containing an array of spatially separated battery cells and a polyorganosiloxane foam material in contact with adjacent battery cells. The polyorganosiloxane foam can contact the battery cells by filling the space between adjacent battery cells with the foam and / or coating the battery cells with the foam. The battery module may further comprise end plates at the inner edges of the shell that contact the battery cells closest to the edges, either directly or indirectly. The foam material can also be inserted into the cavities between adjacent battery cells and between the cells and the end plates, or a foam precursor can be applied over the cells and within the cavities and then cured to form the foam material.

[0016] The foam material of the present invention has been found to provide the desired properties of thermal insulation, flame resistance, and compressibility in LiB thermal barrier applications.

[0017] In the following examples, ViMe 2 SiO 1 / 2 / (CH 3 ) 3 Si - O 1 / 2 / SiO 4 / 2 The M w and M n of the resin were determined by gel permeation chromatography using a gpc column filled with divinylbenzene cross-linked polystyrene bead pore type Mixed-C (Polymer Laboratory) with a size of 5 mm in diameter. THF was used as the mobile phase and detection was performed with a refractive index detector.

[0018] Example 1 - Preparation of a Foamed Organopolysiloxane Article with Ceramic Particles Using a Flacktek Speed Mixer, dimethylvinylsiloxy endblocked polydimethylsiloxane (Polymer 1, 11.3 pbw) having a viscosity of about 40,000 mPas, 1) dimethylvinylsiloxy terminated polydimethylsiloxane having a viscosity of about 1,900 mPa·s and about 0.22 wt% Vi, and 2) 5:40:55 ViMe 2 SiO 1 / 2 :(CH 3 ) 3Si-O 1 / 2 :SiO 4 / 2 Structural unit ratio, M of 5000 n and M of 21,400 w ViMe having 2 SiO 1 / 2 / (CH 3 ) 3 Si-O 1 / 2 / SiO 4 / 2 A 64:36 w / w blend with a resin (polymer - resin blend, 64.9 pbw), and Micral 855 aluminum hydroxide (15.2 pbw) were mixed together to prepare the first component (Part A). The contents were stirred at 2000 rpm for 30 seconds, then a complex of Pt(0) and divinyltetramethyldisiloxane (0.93 pbw, 0.62 wt% Pt), 1,4 - butanediol (2.6 pbw), and benzyl alcohol (3.3 pbw) were added to the mixture, and the contents were stirred at 2000 rpm for 30 seconds. Finally, Elminas Spheres HCMS - W150 hollow ceramic particles (average volume particle size of 100 μm; 20 pbw) were added to the mixture, and the contents were stirred at 2000 rpm for 30 seconds.

[0019] The contents were stirred at 2000 rpm for 30 seconds, then a complex of chloroplatinic acid and divinyltetramethyldisiloxane (0.93 pbw, 0.62 wt% Pt), 1,4 - butanediol (2.6 pbw), and benzyl alcohol (3.3 pbw) were added to the mixture, and the contents were stirred at 2000 rpm for 30 seconds. Finally, Elminas Spheres HCMS - W150 hollow ceramic particles (average volume particle size of 100 μm; 20 pbw) were added to the mixture, and the contents were stirred at 2000 rpm for 30 seconds.

[0020] The second composition (Part B) was similarly prepared by mixing together Polymer 1 (8.9 pbw), a polymer resin blend (51 pbw), and Hymod M855 aluminum hydroxide (26.4 pbw). The contents were stirred at 2000 rpm for 30 seconds, and then a linear organohydrogenpolysiloxane having a viscosity of 30 mPa·s and an SiH content of 1.6 wt% (6.7 pbw), and a polydimethyloorganohydrogensiloxane having a viscosity of 5 mPa·s and an SiH content of 0.7 wt% (5.1 pbw) were added to the mixture, and the contents were stirred at 2000 rpm for 30 seconds. Next, Elminas Spheres HCMS-W150 hollow ceramic particles (20 pbw) were added to the mixture, and the contents were stirred at 2000 rpm for 30 seconds.

[0021] Next, equal amounts of Part A and B were mixed, and the mixture was poured between two release film sheets (matte Mylar film). The initial (pre-foam) thickness was controlled to 0.045 inches using a nip roller. The sample was cured at 70 °C for 5 minutes and then at 100 °C for 15 minutes to produce a foam sheet for further testing. (Density = 0.31 g / cm 3 )

[0022] Example 2 - Preparation of a Foamed Organopolysiloxane Article with Ceramic Particles A process substantially the same as that for preparing the foamed article of Example 1 was carried out, except that Elminas Spheres HCMS THERMO-W75 hollow ceramic particles (average volume particle size of 80 μm, 20 pbw) were used in Parts A and B. (Density = 0.31 g / cm 3 )

[0023] Example 3 - Preparation of a Foamed Organopolysiloxane Article with Ceramic Particles A process substantially the same as that for preparing the foamed article of Example 1 was carried out, except that Elminas Spheres-W300 hollow ceramic particles (average volume particle size of 180 μm, 20 pbw) were used in Parts A and B. (Density = 0.34 g / cm 3 )

[0024] Heat insulation and flammability The foam prepared as described in the examples was tested for heat insulation and flammability using a hot plate placed on a hydraulic press. The hot plate was set at 600 °C, and an insulator was placed on the surface. Four thermocouples (type K) were fixed on an aluminum heat sink (4 inches × 4 inches × 0.47 inches) using Kapton tape. Then, the sample (4 inches × 4 inches) was placed and fixed on the heat sink using Kapton tape. An additional thermocouple (type K) was attached to the sample surface using Kapton tape. The insulator was removed from the hot surface, and the sample attached to the heat sink was quickly placed on the hot surface with the sample surface facing the hot plate surface and the Al heat sink facing the opposite side. The pressure was rapidly increased to 355 kPa. The interface temperature between the hot plate surface and the sample surface, and the interface temperature between the sample surface and the heat sink were recorded using a data logger. When the time reached 300 seconds, the pressure was released and the test was terminated. If the temperature of the sample surface was less than 300 °C, it was considered acceptable. If there was no observable flame throughout the test, it was considered to have acceptable flame resistance.

[0025] Hardness The hardness was measured using a Shore 00 durometer. The test specimen was placed on a hard and flat surface. Next, the indenter of the Shore 00 durometer was pressed against the specimen to ensure that the indenter was parallel to the surface. The hardness was read while in firm contact with the specimen. A hardness less than 80 was considered acceptable.

[0026] Compressive force The compressive force was measured using a TA.HDplus texture analyzer equipped with a 100 kg load cell, an aluminum probe with a diameter of 40 mm, and a flat heavy-duty aluminum substrate. The silicone foam sample was circularly cut using a 1-inch diameter die cut and placed between the substrate and the probe. First, the probe was set at the same height as the sample thickness and lowered at a speed of 1 mm / second until the pressure reached the highest point. The sample thickness and pressure were recorded as a compressive force curve. The pressure at 30% of the original sample thickness was recorded. A compressive force of less than 500 kPa was considered acceptable.

[0027] Density of the foam The foam density was calculated based on the average thickness and weight of two 1-inch diameter foam samples.

[0028] The properties of the ceramic-filled organopolysiloxane article were compared with a commercially available organopolysiloxane article (COHRlastic Silicone Foam, available from Stockwell Elastomerics) that has a structure similar to the foam of the examples except that it does not contain hollow ceramic particles.

[0029] Table 1 is an overview of the performance characteristics of the foams of Examples 1-3 and the commercially available comparative foams. The density was measured in g / cm 3 . The hardness was measured in Shore 00 units. The compressive force (force) was measured in kPa at 30% compression. The temperature at 600 °C (T after 300 seconds) refers to the sample surface temperature after 300 seconds, and the flammability refers to the observability of the flame during the heat insulation test.

[0030]

Table 1

[0031] Table 1 shows that all the foams of the present invention pass all the tests, while the commercial examples fail the heat insulation test. Surprisingly, it has been found that the hollow ceramic particles can lower the surface temperature in 300 seconds without adversely affecting other important properties of the foam. Furthermore, it has been found that a hollow ceramic particle size in the range of 50 μm to 150 μm is particularly effective in lowering the surface temperature.

Claims

**Claim 1** A composition comprising, based on the weight of the composition, a) 2 to 50 weight percent of a polysiloxane functionalized with at least two Si—H groups and having a degree of polymerization in the range of 5 to 1000; b) 1 to 50 weight percent of water, an alcohol, a diol, a polyol, or a compound containing one or more silanol groups; c) 10 to 90 weight percent of a polysiloxane functionalized with at least one ethylenically unsaturated group and having a degree of polymerization in the range of 20 to 2000; (the total concentration of components a, b, and c is in the range of 35 to 95 weight percent based on the weight of the composition) d) a catalytic amount of a hydrosilylation catalyst; e) 1 to 30 weight percent of a flame retardant; f) 1 to 35 weight percent of hollow ceramic particles having a volume average particle diameter in the range of 25 μm to 300 μm; A composition comprising the above components. **Claim 2** The composition according to claim 1, wherein the polysiloxane functionalized with at least two Si—H groups is functionalized with at least three Si—H groups, the total concentration of components a, b, and c is in the range of 50 to 80 percent based on the weight of the composition, and the concentration of the flame retardant is in the range of 2 to 20 weight percent based on the weight of the composition. **Claim 3** The composition according to claim 2, wherein the polysiloxane functionalized with at least one ethylenically unsaturated group is a divinyl-functionalized polydimethylsiloxane having a degree of polymerization in the range of 100 to 1000. **Claim 4** The flame retardant is Al(OH) ３ , Mg(OH) ２ , MgCO ３ ·3H ２ O, Mg ５ (CO ３ ) ４ (OH) ２ ·4H ２ O, MgCa(CO ３ ) ２ , AlO(OH), NaHCO ３ , and hydrated MgSO ４ The composition according to claim 3, which is one or more flame retardants selected from the group consisting of **Claim 5** The composition according to any one of claims 1 to 4, wherein the hollow ceramic particles have an average volume particle diameter by dynamic light scattering in the range of 25 μm to 200 μm. **Claim 6** The composition according to any one of claims 1 to 4, wherein the hollow ceramic particles have an average volume particle diameter by dynamic light scattering in the range of 50 μm to 150 μm. **Claim 7** The hollow ceramic particles are crystalline or semi-crystalline Al ２ O ３ particles, crystalline or semi-crystalline SiO ２ particles, or crystalline or semi-crystalline CaO particles, the composition according to claim 5 or 6. **Claim 8** The composition according to claim 3, wherein the divinyl-functionalized polydimethylsiloxane is a bimodal distribution divinyl-functionalized polydimethylsiloxane having a complex viscosity in the range of 10,000 to 50,000 mPa·s.

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